The choice of the proper cleaning method is important. Some methods leave residues that cause rapid resoiling and defeat the whole purpose of cleaning. Some methods actually damage the carpet fibers. Check your carpet manufacturer recommendations. 

       *Carpet Shampooing or Dry Foam Extraction 
       *Dry Powder
       *Bonnet or Chemical Cleaning 
       *Hot Water Extraction or Steam Cleaning

Shampoo or Dry Foam Extraction: The theory in shampoo methods is to generate a lot of foam in the carpet, allow this foam to dry, have the resulting residue attract soil, and vacuum up the residue and soil the next day. A carpet shampoo must contain a very foamy chemical. The most common is the same as in your hair shampoo, sodium lauryl sulfate or one of its relatives. The problem is that they dry to a soft, sticky residue, which will cause resoiling.

Because shampoos are actually very poor detergents, they frequently also contain high levels of optical brighteners that make the carpet appear cleaner and brighter than it really is, for a while. It may eventually give the carpet a yellow cast that cannot be removed. Carpet manufacturers strongly discourage the use of optical brighteners because of the potential for yellowing.

Shampoo machines are like floor scrubbers with round brush heads. Dry foam extractors use cylindrical brushes and vacuums to remove some of the foam. Aggressive brush agitation required by both shampoo methods can cause permanent pile distortion, especially on cut pile carpet (which most residential carpet is).
 
Shampoo methods are inferior due to poor cleaning results plus, since there is no rinse action, rapid resoiling will occur.

Dry Powder: This method is often called 'dry cleaning' since virtually no water is used.

In this method, dry absorbent compound (containing small amounts of water, detergent, and solvent,) is sprinkled over carpet or worked into the carpet with mechanical agitation from a machine. The absorbent cleaner is most commonly organic, but may also be polymers. They are often used with a detergent prespray in heavily soiled areas.

The theory is that the compound will attract and absorb soil in the carpet, and then be vacuumed away. The carpet must be thoroughly vacuumed before and after cleaning to ensure that all of the compound comes out of the carpet! With extremely fine powder types, indoor air quality can be compromised. If a white powder starts appearing on shoes and cuffs of pants, too much was used and it was not thoroughly vacuumed up.

This cleaning method has the advantage of no drying time for interim maintenance, since little water is used. This makes it a common maintenance cleaner for short commercial carpet. Residential carpets are generally too thick for this system to remove heavy soil. Over use of the brush machine can cause permanent fiber distortion and damage.

Bonnet or Chemical Cleaning: This method is also called 'dry cleaning' which is a misnomer, since water is used. Sometimes carbonated water is used (in theory) to give better soil suspension. Companies using this method frequently use 'scare' tactics in their advertising to convince you that hot water extraction will destroy the carpet.

Bonnet cleaning is simply an adaptation of hard floor spray buffing to carpets. A rotary shampoo buffer is used, but instead of using a brush, a thick round pad is used. The carpet is sprayed with a solution and/or the pads are soaked in the solution and squeezed lightly before being placed under the spinning head. This spinning pad is then expected to absorb all the cleaner and soil from the carpet.

This method has very limited capability for soil removal and leaves much of the detergent in the pile since it employs no real extraction or rinsing. As a result, rapid re-soiling often occurs. Another disadvantage is that the spinning bonnet may distort the fibers of cut pile carpet, fuzzing the pile and leaving distinct swirl marks. Many manufactures recommend against this method of cleaning.

Hot Water Extraction or Steam Cleaning: This is the method nearly all the carpet manufacturers and fiber producers recommend.

This is the only cleaning method classified as 'deep cleaning'. All the others are considered 'light surface cleaning' because they are incapable of removing soil deep in the pile. Also, all the other methods leave large amounts of detergent or cleaning agents in the carpet after cleaning.

The maintenance brochure published by the world's largest carpet manufacturer, Shaw Industries, recommends this method, because its own research indicates that it provides the best capability for cleaning.

This method is frequently called 'steam' cleaning due to the fine spray of hot water that is used. Real steam is a gas rather than a liquid, and is never used on carpet. The process consists of spraying the hot cleaning solution into the carpet pile and recovering the solution and soil with a powerful vacuum into a holding tank. This can be done from a truck-mounted unit outside the home with only the hose and floor tool entering the home or by a portable electric machine which is brought inside the home.

From a health standpoint, the truck-mounted system is preferred because the dirty air and humidity are exhausted outside rather than recirculated around inside the house. Additionally, truck-mounted systems usually are more powerful than portables, do a much better cleaning job, and get the carpet dry more quickly.